Thymoquinone derivatives for treatment of cancer

ABSTRACT

The present invention describes thymoquinone compounds formula (I): (i) These compounds have been identified as being useful in the treatment of cancer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 15/502,944 filed on Feb. 9, 2017, which is a U.S. national phaseapplication of International Patent Application No. PCT/IB2014/063821,filed Aug. 9, 2014, the contents of which are incorporated herein byreference in their entireties.

TECHNICAL FIELD

This invention relates to substituted thymoquinone derivatives. Theinvention also relates to the use of such compounds in the treatment ofcancer and pharmaceutical compositions containing such compounds.

SEQUENCE LISTING

This application contains a sequence listing. The sequence listing filein ASCII text format is named Sequence_Listing_140943_ST25.txt, is 876bytes in size, was created on Jun. 19, 2017, and is incorporated hereinby reference in its entirety.

BACKGROUND ART

Thymoquinone, 2-isopropyl-5-methyl-1,1,4-benzoqinone (TQ), can beextracted from black seed (Nigella sativa) oil and has been reported asan anticancer agent in cancer cells. The anticancer effects of TQ onmalignant tumours with selectivity towards cancer cells over normal cellhas been discussed in Aggarwall B B et al (2008) Planta Med vol. 74(13)pp 1560-1569. Thymoquinone analogs have also been proposed for the usein treating pancreatic cancers, for example in WO2011126544.

The end caps of human chromosomes, telomeres, are known to protect DNAchromosomes against degradation, non-homologous end-stacking andnuclease attacks. Telomeres are shortened after each cell division tillthe cell loses its functions and apotosis. The telomerase enzyme, foundactive in most cancer cells, re-elongates the telomere and maintains itslength causing cancer cell to continue to divide indefinitely. Telomerescomprise tandem repeats enriched in guanine bases that fold up inphysiological conditions to form four-stranded DNA called G-quadruplex.Folding single stranded telomeric DNA into G-quadruplex structure hasbeen shown to inhibit the telomerase enzyme, overexpressed in cancercells.

Small molecules that bind and stabilise G-quadruplex DNA have been foundto inhibit the telomerase enzyme in cancer cells and subsequentlyinhibit DNA replication and cancer cell proliferation, Huppert J L(2007), Phil. Trans. A. Math. Phys. Eng. Sci., vol. 365(1861) pp2969-2984. Therefore molecules with high preferential affinity towardsG-quadruplex DNA have been seen as a potential avenue of compounds fordeveloping new anticancer therapeutic agents.

Accordingly it is an object of the invention to provide furtherthymoquinone derivatives that may be effective in cancer treatment.

SUMMARY OF INVENTION

The present invention relates to compounds of formula (I):

-   and to pharmaceutically salts or solvates thereof wherein:-   R₁ and R₂ are independently selected from C₁-C₆ alkyl, wherein R₁    and R₂ are different;-   X is NR₃R₄, wherein:    -   R₃ is selected from H or —(CH₂)₂—OH; and    -   R₄ is selected from H or —(C₁-C₄alkyl)R₅, wherein:        -   R₅ is selected from:        -   a) —OH,        -   b) phenyl, wherein phenyl is optionally substituted by 1-3            substituents independently selected from —CF₃, —F, —OCH₃,            —NH₂ and —SO₂NH₂,        -   c) a 5 or 6 membered heterocyclic ring having 1 or 2 hetero            atoms selected from O and N, and wherein the heterocyclic            ring is optionally substituted by 1-2 substituents            independently selected from —OH and CH₃,        -   d) a ring system having the formula of:

-   -    and        -   e) NR₆R₇, wherein:            -   R₆ is selected from H or CH₃; and            -   R₇ is selected from CH₃, phenyl, and a ring system                having the formula of:

-   -    wherein the ring system is optionally substituted by 1-2        substituent of CH₃; and

-   Y is H.

In a preferred embodiment R₁ is CH₃, or isopropyl. More preferably R₁ isCH₃.

In a preferred embodiment R₂ is CH₃, or isopropyl. More preferably R₂ isisopropyl.

In a particularly preferred embodiment R₁ is CH₃ and R₂ is isopropyl.

In a preferred embodiment R₃ is H.

In a preferred embodiment R₄ is —(C₁-C₄alkyl)R₅. More preferably R₄ is—(C₁-C₂alkyl)R₅.

In a preferred embodiment R₅ is selected from:

-   a) —OH,-   b) phenyl, wherein phenyl is optionally substituted by 1-3    substituents independently selected from —CF₃, —F, —OCH₃, —NH₂ and    —SO₂NH₂,-   c) a 5 or 6 membered heterocyclic ring selected from morpholinyl,    pyranyl, piperidinyl, pyrrolidinyl, piperazinyl, pyridinyl, and    pyrimidinyl, wherein the heterocyclic ring is optionally substituted    by 1-2 substituents independently selected from —OH and CH₃.-   d) a ring system having the formula of:

-    and-   e) NR₆R₇, wherein:    -   R₆ is selected from H or CH₃; and    -   R₇ is selected from CH₃, phenyl, and a ring system having the        formula of:

-   -   wherein the ring system is optionally substituted by 1-2        substituent of CH₃.

In one embodiment wherein R₅ is a 5 or 6 membered heterocyclic ring, the5 or 6 membered heterocyclic ring is selected from morpholinyl, pyranyl,piperidinyl, pyrrolidinyl, piperazinyl, each optionally substituted by—OH or the heterocyclic ring is selected from pyridinyl, andpyrimidinyl, wherein the pyrimidinyl is optionally substituted with —OHand CH₃.

In a particularly preferred embodiment R₄ is H or —(C₁-C₂alkyl)R₅,wherein R₅ is selected from OH, morpholinyl and phenyl, wherein thephenyl is optionally substituted with 1 or 2 substituents selected from—CF₃, —F and —OCH₃.

In one embodiment when R₃ is H, R₄ is preferably H or —(C₁-C₂alkyl)R₅,wherein R₅ is selected from morpholinyl and phenyl, wherein the phenylis optionally substituted with 1 or 2 substituents selected from —CF₃,—F and —OCH₃.

Particularly preferred compounds of the invention include:

-   5-Isopropyl-2-methyl-3-((2-morpholinoethyl)amino)-1,4-benzoquinone-   5-Isopropyl-2-methyl-3-(4-trifluoromethylbenzylamino)-1,4-benzoquinone-   5-Isopropyl-2-methyl-3-(4-fluorobenzylamino)-1,4-benzoquinone-   5-Isopropyl-2-methyl-3-(benzylamino)-1,4-benzoquinone-   5-Isopropyl-2-methyl-3-(3,5-ditrifluoromethylbenzylamino)-1,4-benzoquinone-   5-isopropyl-2-methyl-3-(2-hydroxyethylamino)-1,4-benzoquinone-   5-isopropyl-2-methyl-3-(3,4-dimethoxylbenzylamino)-1,4-benzoquinone-   3-amino-5-isopropyl-2-methyl-1,4-benzoquinone.

A particularly preferred compound is3-amino-5-isopropyl-2-methyl-1,4-benzoquinone.

Suitable salts include salts of acidic or basic groups present incompounds of formula (I). The compounds of formula (I) that are basic innature are capable of forming a wide variety of salts with variousinorganic and organic acids. The acids that may be used to preparepharmaceutically acceptable acid addition salts of such basic compoundsof formula (I) are those that form non-toxic acid addition salts.Suitable salts include acetate, benzensulfonate, benzoate, bicarbonate,bisulfate, bitartrate, borate, bromide, calcium edentate, camsylate,carbonate, chloride, clavulanate, citrate, dihydrochloride edentate,edisylate, estolate, esylate, ethylsuccinate, fumarate, gluceptate,gluconate, glutamate, glycollylarsanilate, hexylresorcinate,hydrabamine, hydrobromide, hydrochloride, iodide isothionate, lactate,lactobionate, laurate, malate, maleate, mandelate, mesylate,methylsulfate, mucate, napsylat, nitrate, oleate, oxalate, pamoate,palmitate, pantothenate, phosphate, diphosphate, diphosphate,polygalacturonate, salicylate, stearate, subacetate, succinate, tannate,tartrate, teoclate, tosylate and valerate.

The compounds of the present invention may be synthesised by a number ofsynthetic routes. In one method of making the compounds of theinvention, thymoquinone derivatives can be synthesised as shown inScheme I, wherein R₁, R₂, R₃ and R₄ are defined herein.

Compounds of formula (I) may be synthesised in a one pot reaction byreacting thymoquinone in a suitable solvent such as methanol, with theappropriate amine, NH₂R₃R₄, dissolved in a suitable solvent. The mixtureis reacted in the presence of air at room temperature. The solvent isthen concentrated and purified and the resultant products arecrystallized.

An alternative route for synthesising a thymoquinone derivative offormula (III) is shown in scheme (II).

Compounds of formula (III) may be synthesised by reacting thymoquinonewith dimethoxybenzylamine in a solvent, such as methanol. The mixture isreacted in the presence of air at room temperature resulting in theformation of a compound of formula (IV). The mixture is allowed todecompose and a product of formula (III) is formed. The solvent is thenconcentrated and purified and the resultant product is crystallised.

These compounds have been found to selectively bind G-quadruplex DNA andstabilise their structure. Stabilisation of the G-quadruplex structurecan inhibit the telomerase enzyme, and therefore the compounds may playa role in the treatment of cancer.

The invention also relates to compounds of formula (I) as describedabove for use in the treatment of cancer. In particular the compoundsare particularly useful in the treatment of pancreatic cancer, lungcancer, prostate cancer and breast cancer.

The invention also provides a method of treating cancer in a mammal,particularly a human, comprising administering to the mammal an amountof a compound of formula (I) as defined above, or a pharmaceuticallyacceptable salt or solvate thereof. The compound may be administered ina therapeutically effective amount.

The invention further relates to the compounds of formula (I) incombination with at least one suitable anti-tumour or neoplastic agentfor the treatment of cancer, in particular for the treatment ofpancreatic, lung, prostate or breast cancer.

The term “treatment” shall be interpreted to include curing, reversing,alleviating, and/or palliative treatment of the condition.

A “therapeutically effective amount” of a compound is an amount of thecompound, which when administered to a subject, is sufficient to conferthe intended therapeutic effect. A therapeutically effective amount canbe given in one or more administrations.

Common cancers would include, bladder, breast, colon, rectal,endometrial, kidney (renal cell), leukaemia, lung, melanoma, non-Hodgkinlymphoma, pancreatic, prostate, brain, skin, liver and thyroid cancers.

Patients suffering from cancer are commonly co-administered additionaltherapeutic agents, in particular suitable antineoplastic or anti-tumouragents. Suitable co-administrants would include:

-   1. Alkylating antineoplastic agents: such as cisplatin, carboplatin,    oxaliplatin, mechlorethamine, cyclophosphamide, chlorambucil, and    ifosfamide.-   2. Plant alkaloids and terpenoids. These include:    -   i. vinca alkaloids such as vincristine, vinblastine, vinorelbine        and vindesine    -   ii. podophyllotoxins such as etoposide and teniposide    -   iii. taxanes, such as paclitaxel, originally known as taxol, and        docetaxel.-   3. Topoisomerase inhibitors:    -   i. type I topoisomerase inhibitors include camptothecins:        irinotecan and topotecan    -   ii. type II inhibitors include amsacrine, etoposide, etoposide        phosphate, and teniposide-   4. Cytotoxic antibiotics such as actionmycin, anthracyclins,    doxorubicin, daunorubicin, valrubicin and epirubicin. Other cytoxic    antibiotics include bleomycin, plicamycin and mitomycin.

Other therapeutic agents are commonly administered to patients to dealwith the side effects of chemotherapy. Such agents might includeanti-emetics for nausea, or agents to treat anaemia and fatigue. Othersuch medicaments are well known to physicians and those skilled incancer therapy.

Such agents may be administered sequentially, simultaneously orconcomitantly.

The invention also relates to a pharmaceutical composition comprising acompound of formula (I) as described above, or a pharmaceuticallyacceptable salt or solvate thereof and a pharmaceutically acceptablediluents or carrier.

The pharmaceutical composition may comprise an additional therapeuticagent.

Suitable composition forms include forms suitable for oraladministration such as tablets, capsule, pills, powders, sustainedrelease formulations, solutions, and suspension, for parental injectionsuch as sterile saline solutions, suspensions or emulsion; for topicaladministration such as ointments or creams; or rectal administrationsuch as suppositories.

Exemplary parenteral administration forms include suspensions orsolutions in sterile aqueous solutions, for example aqueous propyleneglycol or dextrose solutions. Such dosage forms can be suitablybuffered, if desired.

Suitable pharmaceutical carriers include inert diluents or fillers,water and various organic solvents. Compositions may also includeadditional ingredients such as flavouring, binders, and excipients.Tablets may include: disintegrates such as starch, alginic acid andcomplex silicates; binding agents such as sucrose, gelatine and acacia,and lubricating agents such as magnesium stearate, sodium laurylsulphate and talc.

Solid compositions may also include soft and hard gelatin capsules.Preferred materials include lactose, milk sugars and high molecularweight polyethylene glycols.

Aqueous suspensions or elixirs may include sweetening or flavouringagents, colours and dyes, emulsifying agents, suspending agents as wellsas diluents such as water, ethanol, propylene glycol, glycerin orcombinations thereof.

Pharmaceutical forms suitable for the delivery of the compounds of thepresent invention and methods of preparing the various pharmaceuticalcompositions will be readily apparent to those skilled in the art. Suchcompositions and methods for their preparations may be found, forexample in Remington's Pharmaceutical Sciences, 19^(th) Edition (MackPublishing Company 1995).

FIGURES

FIGS. 1A and 1B shows inhibition of cellular viabilities by compounds TQ1-5 in A540 cells (FIG. 1A) and TQ8 in A549, MDA-MB-231, and HT29 cells(FIG. 1B). Cells were treated at the indicated concentrations ofcompounds TQ 1-5 and 8 or with vehicle (0.1% DMSO) as a control.Columns, mean; bars S.E.M.

FIG. 2 shows fluorescence titrations of compounds TQ1-8 (5×10−6M) (a-hrespectively) with G-quadruplex. TQs were excited at 279, 280, 280, 278,280, 280, 280 and 327 nm respectively with 10 nm slits width. The insetrepresents a plot for fluorescence titrations using modified Scatchardequation.

FIG. 3 shows the fluorescence spectra of 5′-Flu-G-quadruplex (2×10−6 M)with compounds TQ1-8. 5′-Fl-G-quadruplex was excited at 494 nm andemitted at 518 nm.

FIG. 4 shows the CD spectra of G-quadruplex (4×10⁻⁶ M) with compoundsTQ1-8 (a-h respectively).

FIG. 5 shows the melting curve for G-quadruplex DNA and its complexeswith compounds TQ1-8.

FIG. 6 shows the selectivity of compounds TQ1-8 toward G-quadruplex(5′-Flu-TelQ, 1×10−7 M) in presence of 0, 10, 50 and 100 folds of ct-DNA(A) and telomere dsDNA (B).

EXPERIMENTAL

The synthesis of various compounds of the present invention is describedby way of example.

Synthesis of Thymoquinone Derivatives

5 mmol thymoquinone (821 mg) (Frinton Laboratories Inc, USA) wasdissolved in methanol (50 mL) into a two necks flask (100 mL). The aminesolution (5 mmol), (2-aminoethylmorpholine, benzylamine,4-(trifluoromethyl) benzylamine, 3,5-bis(trifluoromethyl)benzylamine,3,4-dimethoxybenzylamine, 4-fluorobenzyl-amine or 2-aminoethanol(Sigma-Aldrich)), dissolved in methanol (5 mL), was added drop wise tothe thymoquinone solution.

The reaction mixture was stirred and air bubbled at room temperature forup to 3 days during which the reaction progress was monitored using TLC.The solvent was concentrated under vacuum and the product was purifiedon silica gel column using hexane:ethyl acetate (6:4 v/v) as mobilephase.

This general procedure was applied for the synthesis of compoundsTQ1-TQ7. Compound 3-aminothymoquinone (TQ8) was prepared as describedbelow.

3-aminothymoquinone (TQ8) was synthesized by allowing thymoquinone (5mmol, 821 mg) to react with 3,4-dimethoxybenzylamine (5 mmol, 777 μL) inmethanol (5 mL) as per the procedure above. The solution was stirred andair bubbled at room temperature for 5 days during which the reaction wasmonitored by TLC.

Initially, 3′,4-dimethoxybenzylamino-thymoquinone (TQ7) is formed andthen hydrolyzed to form 3-aminothymoquinone (TQ8). Oxidation of3′,4-dimethoxybenzylamino-thymoquinone (TQ7) results in the formation ofthe hydroxymethyl-amino intermediate which upon rearrangement produced3-aminothymoquinone (TQ8) and 3,4-dimethoxybenzaldehyde.

The solvent was concentrated under vacuum followed by purifying theproduct over silica gel column using hexane:ethyl acetate (7:3 v:v) asmobile phase. The pink layer was separated into two layers, the firstreleased is for TQ7 and the second released is for TQ8. R_(f) for thecompound TQ8 is 0.662.

The mechanism for the formation of 3-aminothymoquinone (TQ8) is shown inScheme (III).

The obtained products were crystallized from the same solvent and theirstructure was confirmed using IR, ¹H-NMR and ¹³C-NMR, MS spectrometryand elemental analysis. Table 1 shows the reaction times, melting pointsand reaction yields of the newly synthesized thymoquinone aminederivatives.

Reaction times between 24 hours and 5 days were found necessary fordifferent products with melting temperatures of 68-114° C. and reactionyields between 45.2-73.8% obtained.

TABLE 1 Com- Reaction pound Aryl-amine Time M.P. ° C. Yield TQ1

48 hrs 92-95 68.3% TQ2

64 hrs 110.5- 112 50.1% TQ3

72 hrs 80-82.5 45.2% TQ4

72 hrs 83-84.5 73.6% TQ5

48 hrs 111-114 47.2% TQ6

36 hrs Oil 66.7% TQ7 TQ8

24 hrs 5 days Oil 68-72 61.1% 52.3%

The results of the elemental and spectral analyses of the synthesizedthymoquinone derivatives (TQ1-TQ8) are provided below:

Example 1:5-Isopropyl-2-methyl-3-((2-morpholinoethyl)amino)-1,4-benzoquinone (TQ1)

The compound of example 1 (TQ1) was separated by silica gel columnchromatography using hexane/ethyl acetate 6:4 as a mobile phase.

R_(f) for the product is 0.235. It was obtained as dark violet crystalsafter 48 hrs, yield 68.3%, mp 92-95° C.; IR (KBr, ν cm⁻¹): 3306 (N—H),1650 and 1615 (C═O), 1118 (C—O—C); ¹H NMR (400 MHz, DMSO-d₆) δ ppm 1.03(6H, d, J=6.8 Hz) 1.93 (3H, s) 2.36 (4H, t, J=4.6 Hz) 2.47 (2H, t, J=6.8Hz) 2.85 (1H, m) 3.50-3.56 (6H, m) 6.27 (1H, t, J=5.6 Hz) 6.33 (1H, s);¹³C NMR (400 MHz, DMSO-d₆) δ ppm 10.07, 21.56, 26.44, 41.24, 53.32,57.83, 66.7, 107.81, 132.7, 145.58, 149.79, 184.73, 185.69. EI-MS: m/z292.2, 0.9% (M⁺), 232.1, 23.1%, 206.1, 61.1%, 149.0, 67.6%, 100, 100%.Elemental analysis (C₁₆H₂₄N₂O₃), calculated: C, 65.73%; H, 8.27%; N,9.58%. Found: C, 66.57%; H, 8.72%; N, 8.59%.

Example 2:5-Isopropyl-2-methyl-3-(4-trifluoromethylbenzylamino)-1,4-benzoquinone(TQ2)

The compound of example 2 (TQ2) was purified by silica gel columnchromatography using hexane/ethyl acetate 8:2 as a mobile phase.

R_(f) for the product is 0.485. It was obtained as dark red crystalsafter 64 hrs, yield 50.1%, mp 110.5-112° C.; IR (KBr, ν cm⁻¹): 3313(N—H), 1666 and 1649 (C═O); ¹H NMR (400 MHz, DMSO-d₆) δ ppm 1.00 (6H, d,J=6.8 Hz) 1.77 (3H, s) 2.84 (1H, m) 4.72 (2H, d, J=7.6 Hz) 6.31 (1H, s)7.08 (1H, t, J=7.4 Hz) 7.44 (2H, d, J=8.0 Hz) 7.68 (2H, d, J=8.4 Hz);¹³C NMR (400 MHz, DMSO-d₆) δ ppm 9.81, 21.44 26.41, 47.24, 108.24,125.78, 125.81, 127.47, 127.99, 132.19, 145.36, 146.22, 150.07, 184.78,185.69. EI-MS: m/z 337.3, 94.4% (M⁺), 322.2, 24.1%, 192.1, 100%, 178.1,46.3%, 159.0, 46.3%. Elemental analysis (C₁₈H₁₈F₃NO₂), calculated: C,64.09%; H, 5.38%; N, 4.15%, Found: C, 65.15%; H, 5.34%; N, 3.76%.

Example 3: 5-Isopropyl-2-methyl-3-(4-fluorobenzylamino)-1,4-benzoquinone(TQ3)

The compound of example 3 (TQ3) was separated by silica gel columnchromatography using hexane/ethyl acetate 7:3 as a mobile phase.

R_(f) for the product is 0.530. It was obtained as dark red crystalsafter 72 hrs, yield 45.2%, mp 80-82.5° C.; IR (KBr, cm⁻¹): 3315 (N—H),2967, 1667 and 1650 (C═O); ¹H NMR (400 MHz, DMSO-d₆) δ ppm 1.00 (6H, d,J=6.4 Hz) 1.79 (3H, s) 2.84 (1H, m) 4.61 (2H, d, J=6.4 Hz) 6.30 (1H, s)6.95 (1H, t, J=8.0 Hz) 7.13 (2H, t, J=8.0 Hz) 7.25 (2H, t, J=8.0 Hz);¹³C NMR (400 MHz, DMSO-d₆) δ ppm 9.88, 21.45, 26.42, 46.91, 108.14,115.55, 115.76, 128.74, 128.82, 132.29, 137.22, 145.35, 150, 160.34,162.75, 184.81, 185.71. EI-MS: m/z 287.2, 100% (M⁺), 272.2, 35.2%,192.1, 46.3%, 178.1, 57.4%, 109.0, 97.2%. Elemental analysis(C₁₇H₁₈FN0₂), calculated C, 71.06%; H, 6.31%; N, 4.87%, Found: C,72.16%; H, 6.95%; N, 5.67%.

Example 4: 5-Isopropyl-2-methyl-3-(benzylamino)-1,4-benzoquinone (TQ4)

The compound of example 4 (TQ4) was purified by column chromatographyusing hexane/ethyl acetate 8:2 as a mobile phase.

R_(f) for the product is 0.636. It was obtained as dark red crystalsafter 72 hrs, yield 73.6%, mp mp 83-84.5° C.; IR (KBr, cm⁻¹): 3312(N—H), 2966, 1665 and 1650 (C═O); ¹H NMR (400 MHz, DMSO-d₆) δ ppm 1.00(6H, d, J=6.8 Hz) 1.80 (3H, s) 2.84 (1H, m) 4.63 (2H, d, J=7.2 Hz) 6.30(1H, s) 6.95 (1H, t, J=7.0 Hz) 7.19-7.23 (3H, m) 7.28-7.32 (2H, m); ¹³CNMR (400 MHz, DMSO-d₆) δ ppm 9.87, 21.44, 26.42, 47.53, 107.84, 126.74,127.24, 128.93, 132.37, 141.08, 145.41, 149.91, 184.82, 185.69. EI-MS:m/z 269.2, 100% (M⁺), 254.2, 30.6%, 192.1, 75.0%, 178.1, 45.4%, 91.0,81.5%. Elemental analysis (C₁₇H₁₉NO₂): calculated C, 75.81%; H, 7.11%;N, 5.2%. Found: C, 76.95%; H, 7.39%; N, 5.62%.

Example 5:5-Isopropyl-2-methyl-3-(3,5-ditrifluoromethylbenzylamino)-1,4-benzoquinone(TQ5)

The compound of example 5 (TQ5) was purified by column chromatographyusing hexane/ethyl acetate 8:2 as a mobile phase.

R_(f) for the product is 0.485. It was obtained as dark red crystalsafter 48 hrs, yield 47.2%, mp 111-114° C.; IR (KBr, cm⁻¹): 3319 (N—H),2974, 1677 and 1649 (C═O); ¹H NMR (400 MHz, DMSO-d₆) δ ppm 1.00 (6H, d,J=6.8 Hz) 1.77 (3H, s) 2.84 (1H, m) 4.76 (2H, d, J=7.6 Hz) 6.31 (1H, s)7.02 (1H, t, J=7.2 Hz) 7.95 (3H, s) 7.96 (3H, s); ¹³C NMR (400 MHz,DMSO-d₆) δ ppm 9.97, 21.4, 26.41, 47.18, 109.73, 121.04, 122.44, 125.16,127.9, 130.45, 130.78, 131.85, 145.01, 145.72, 150.38, 184.82, 185.79.EI-MS: m/z 405.2, 0% (M⁺), 390.2, 75.0%, 321.2, 31.5%, 242.1, 100%,227.1, 44.4%, 192.1, 36.1%, 178.2, 21.3%, 148.1, 18.4%. Elementalanalysis (C₁₉H₁₇F₆NO₂): calculated C, 56.3%; H, 4.23%; N, 3.46%. Found:C, 57.05%; H, 4.10%; N, 2.64%.

Example 6: 5-isopropyl-2-methyl-3-(2-hydroxyethylamino)-1,4-benzoquinone(TQ6)

The compound of example 6 (TQ6) was purified by silica gel columnchromatography using hexane/ethyl acetate 9:1 then 7:3 as a mobilephase.

R_(f) for the product is 0.524. It was obtained as dark violet gum after36 hrs, yield 66.7%; IR (KBr, cm⁻¹): 3408.7 (N—H), 2925, 1665.4, 1649.3(C═O); ¹H NMR (400 MHz, CHLOROFORM-d) δ ppm 1.09 (6H, d, J=6.4 Hz) 2.04(3H, s) 2.95 (1H, m) 3.64 (2H, t, J=5.0 Hz) 3.82 (2H, t, J=5.2 Hz) 5.70(1H, s) 6.39 (1H, s); ¹³C NMR (400 MHz, CHLOROFORM-d) δ ppm 10.32,21.31, 26.51, 46.97, 61.92, 109.19, 132.88, 144.70, 149.97, 184.72,186.89. EI-MS: m/z 223.2, 23.8% (M⁺), 192.1, 100%, 177.1, 13.8%, 149.1,11.0%. Elemental analysis (C₁₂-C₁₇NO₃): calculated: C, 64.55%; H, 7.67%;N, 6.27%; O, 21.50%.

Example 7: 5isopropyl-2-methyl-3-(3,4-dimethoxybenzylamino)-1,4-benzoquinone (TQ₇)

The compound of example 7 (TQ7) was purified by silica gel columnchromatography using hexane/ethyl acetate 1:1 as a mobile phase.

R_(f) for the product is 0.524. It was obtained as dark red gum after 24hrs, yield 61.1%; IR (KBr, cm⁻¹): 3394 (—H), 2926, 1649 (C═O); ¹H NMR(400 MHz, CHLOROFORM-d) δ ppm 1.08 (6H, d, J=6.8 Hz) 2.05 (3H, s) 2.94(1H, m) 3.85 (6H, s) 4.57 (2H, d, J=3.6 Hz) 5.64 (1H, s) 6.39 (1H, s)6.72-6.87 (3H, m); ¹³C NMR (400 MHz, Chloroform-d) δ ppm 10.27, 21.30,26.51, 49.13, 55.88, 109.21, 110.31, 111.35, 119.48, 131.07, 132.96,144.37, 149.28, 149.85, 184.49, 186.91. EI-MS: m/z 329.2, 0% (M⁺),314.2, 286.1, 192, 178.1, 137.1. Elemental analysis (C₁₉H₂₃NO₄):calculated: C, 69.28%; H, 7.04%; N, 4.25%; O, 19.43%.

Example 8: (3-amino-5-isopropyl-2-methyl-1,4-benzoquinone (TQ8)

The compound of example 8 (TQ8) was obtained as dark violet crystals,yield 52.3%, mp 68-72° C.; IR (KBr, cm⁻¹): 3461 and 3328 (N—H₂), 2966,1673 and 1649 (C═O); ¹H NMR (400 MHz, DMSO-d₆) δ ppm 1.02 (6H, d, J=7.2Hz) 1.69 (3H, s) 2.84 (1H, m) 6.25 (1H, d, J=1.2 Hz) 6.43 (2H, s,exchangeable with D₂O); ¹³C NMR (400 MHz, DMSO-d₆) δ ppm 8.97, 21.47,26.3, 106.99, 132.37, 145.49, 149.54, 183.99, 185.41. EI-MS: m/z 179.2,100% (M⁺), 164.1, 36.7%, 136.1, 62.4%, 108.1, 38.5%. Elemental analysis(C₁₀H₁₃NO₂): calculated C, 67.02%; H, 7.31%; N, 7.82%. Found: C, 66.65%;H, 7.15%; N, 7.81%.

Effects of Synthesized Compounds on Cancerous Cell Lines CellularViability

Human lung cancer cells A549, human breast cancer cells MDA-MB-231 andcolorectal cancer cells HT29, were used to test the antiproliferativeactivity of the synthesised compounds. Human lung cancer cells A549 weremaintained in RPMI 1640 medium (Hyclone Laboratories, USA), human breastcancer cells MDA-MB-231 and colorectal cancer cells HT29 were maintainedin DMEM medium (Hyclone Laboratories, USA). All media was supplementedwith antibiotics (penicillin 50 U/ml; streptomycin 50 ug/ml) (HycloneLaboratories, USA).

Cells were seeded at a density of 5,000 cells/well into 96-well plates.After 24 h, cells were treated for 24 and 48 h with differentconcentrations of compounds TQ1-5 and 8 (5-100 μM), in triplicate.Control cultures were treated with 0.1% DMSO. The effect of thecompounds TQ1-8 on cell viability was determined using the CellTiter-GloLuminescent Cell Viability assay (Promega Corporation, Madison, USA),based on quantification of ATP, which signals the presence ofmetabolically active cells. The luminescent signal was measured usingthe GLOMAX Luminometer system. Data were presented as proportionalviability (%) by comparing the treated group with the untreated cells,the viability of which is assumed to be 100%.

The anticancer effects of the compounds were tested on human lung cancercell line (A549), breast cancer cell (MDA-MB-231) and colorectal cancercell lines (HT29) using cell viability assay.

FIGS. 1A and 1B show the effects of compounds TQ 1-5 and 8 on the cellviabilities of human lung cancer cell line, A549, using 5, 50 and 100 μMconcentrations. Values are recorded relative to the control sample(DMSO).

Decreases in cellular viability of cancerous cells are observed withincreasing drug concentration and time of exposure (24-48 hours). Thesix compounds at 100 μM concentrations gave steady decreases in cellviability after 24 hours by 15, 32, 29, 17, 33 and 99% relative to thecontrol (DMSO), respectively. After 48 hours exposure, further decreasesof 33, 57, 64, 58, 48 and 100% in cell viability were observed.

These results indicate a toxic effect against lung cancer cells forcompounds TQ1-5 and TQ8. TQ8 had the highest toxic effect of thederivatives tested with cell viability close to zero relative to thecontrol after 24 hours. Compound TQ8 was further tested on breast andcolorectal cancer cell lines. All experiments were repeated at leastthree times.

FIG. 1B shows the effects of compound TQ8 on the cellular viability ofMDA-MB-231 and HT29 cells over 24 and 48 hours using 5-100 μMconcentrations. A concentration and time-dependent decrease in cellviability was observed. The losses in cell viability were 83% and 97%using 24 hours exposure at 100 μM concentrations. These losses increasedto 98% and 99% after 48 hours exposure for MDA-MB-231 and HT29 celllines, respectively.

Compound TQ8 showed the best potency among the eight synthesizedthymoquinone derivatives against examined cancerous cell lines. Acomplete suppression of cell viability was observed at 48 hours using100 μM. The relative cytotoxic effect of compound TQ8 on tested cancercell lines was found in the following order A549>MDA-MB-231>HT29.

An IC50 gives a good estimate of the cytotoxic potency of differentdrugs against cancer cells. The IC50s (concentration produces 50%inhibition in cells viabilities) for compounds TQ1-5 and TQ8 at 24 hoursare shown in Table 2.

The results ranged from 35.01-105.05 μM for tested thymoquinonederivative compounds against A549 cell line. TQ8 gave IC50s of 35.01,45.14 and 55.81 μM against A549, MDA-MB-231 and HT29 cells,respectively. These results indicate good IC-50 values against thetested cells lines.

These results also indicate that compound TQ8 is ≥200% potent comparedto the parent TQ molecule whose IC50 has been reported as 78.34 μMagainst A549 cells.

TABLE 2 IC50s of thymoquinone derivatives IC 50 (μM) Compound A 549 MDA231 HT29 TQ 78.34 — — TQ1 74.32 — — TQ2 84.29 — — TQ3 83.19 — — TQ488.65 — — TQ5 105.05 — — TQ8 35.01 45.14 55.81

The cytotoxic effects for the compounds seen against the cancer cellsindicate that the compounds could be suitable in the use of thetreatment of cancers.

The compounds of the invention, TQ1-8, may be particularly good in invivo models.

Interaction of G-Quadruplex DNA with TQ Ligands

Several mechanisms have been suggested for the anti-tumour effects ofthymoquinone compounds. Stabilising the formation of G-quadruplex DNAstructures with small molecules has been found to inhibit the telomeraseenzyme found in active cancer cells, and has been seen as an effectiveapproach for developing anticancer molecules. Therefore the thymoquinonederivatives were tested for their binding affinity and selectivitytowards G-quadruplex DNA.

DNA solutions for use in the following assays were prepared as describedbelow:

Calf Thymus DNA (Ct-DNA)

A 1000 μg/ml calf thymus ds-DNA was prepared by dissolving 10 mg of DNA(Sigma-Aldrich) into 10 ml Tris-KCl buffer, pH 7.4, without sonicationor stirring. The solution was gently inverted overnight at 4° C. tocompletely solubilize the DNA and prevent shearing of the large genomicDNA. Resultant ct-DNA solutions are stable at 4° C. for several months.

Single Stranded DNA

Purchased synthetic nucleic acids primers (AlphaDNA, Canada) with humantelomere sequence; 5′-AGGGTTAGGGTTAGGGTTAGGG-3′ (SEQ ID NO:1), itsfluorescein labelled 5′ primer 5′-Fl-AGGGTTAGGGTTAGGGTTAGGG-3′ (SEQ IDNO: 2) or its complementary strand 3′-TCCCAATCCCAATCCCAATCCC-5′ (SEQ IDNo: 3) were reconstituted by centrifugation for 10 min at 7000 rpm tocollect the DNA into the vials' bottoms. A 2.00 ml Tris-KCl buffer, pH7.4, was added to each vial, left 2 min for rehydration then vortexedfor 30 seconds. Reconstituted primers were kept overnight at 4° C.before use. Stability of reconstituted primers is more than 6 months.

G-Quadruplex DNA

A 2 ml of the stock single stranded DNA; 5′-AGGGTTAGGGTTAGGGTTAGGG-3′(SEQ ID NO: 1) was gently heated up to 95° C., incubated for 10 minutesand then left to cool to room temperature. Resultant solution was keptin fridge at 4° C. overnight.

Hybridization of Telomeric DNA

A 10⁻⁴ M telomeric dsDNA was prepared by mixing equimolar amounts of5′-AGGGTTAGGGTTAGGGTTAGGG-3′ (SEQ ID No: 1) (268.80 μL of 7.44×10⁻⁴ M)and complementary strand 3′-TCCCAATCCCAATCCCAATCCC-5′(SEQ ID NO: 3)(738.0 μL of 2.71×10⁻⁴ M). The solution was made up to 2 ml usingKCl-Tris-Cl buffer, pH 7.4, vortexed for 15 seconds, incubated at 95° C.for 10 min and left to cool to room temperature. Resultant hybridizeddsDNA was kept at 4° C. until use.

Concentrations of reconstituted stock DNA solutions were determined bydiluting 10 μl of each solution to 1 ml using KCl buffer, pH 7.4.Solutions were vortexed for 15 seconds and its absorbance were measuredat 260 and 280 nm. Concentrations were calculated usingC(μg/ml)=A260×weight per OD×dilution factor, where A is the absorbanceat 260 nm. The purity of oligonucleotides was estimated based on theratio A260/A280. Ratios ≥1.8 were considered enough to indicate highpurity. Since G-quadruplex DNA is formed by folding up from singlestrands, its concentration was similar to that of its single strandedDNA.

TQ Stability

The stability of the thymoquinone derivatives in Tris-KCl buffer, pH 7.4at room temperature were investigated using UV-Vis spectrophotometry.Solutions were found stable and no change in absorbance for up to 12hrs. However, decay in absorbance was observed when solutions kept forlonger times. Therefore, freshly prepared solutions were usedthroughout.

To confirm an interaction between the thymoquinone derivatives andG-quadruplex DNA, this interaction was studied using fluorescence,fluorescence quenching and circular dichroism spectroscopies

Fluorescence Titration

To 3 ml of 5×10⁻⁵ M of each of compounds TQ1-8 in Tris-KCl-buffer, pH7.4, successive portions of G-quadruplex DNA (1.44×10⁻⁴ M) were added.After each addition, the TQ solution was stirred for 20 seconds,incubated for 3 min and its emission was scanned in the range 300-600 nmusing excitation Amax of 280 nm and slit width of 10.00 nm. Titrationstopped when no change in fluorescence intensity was observed.

The results are shown in FIG. 2. Fluorescence titrations of compoundsTQs 1, 2, 4, 5 and 7 with G-quadruplex DNA showed decrease influorescence intensity and red shifts by 24, 14, 30, 25 and 41 nm (FIGS.2a, 2b, 2d, 2e and 2g ). Compounds TQ3 and TQ6 showed a hypochromicityand red shifts by 4 nm and the appearance of a new peak at 353.7 and 350nm respectively (FIGS. 2c and 2f ). Compound TQ6 showed an isosbesticpoint at 315 nm. Compound TQ8 showed an increase in fluorescenceintensity with slight red shift (FIG. 2h ). These changes influorescence spectra of TQs during titration indicated the binding ofTQs with G-quadruplex DNA. The isosbestic point indicates an equilibriumprocess during binding interaction.

Quenching Assay of Fluorescein Labelled G-Quadruplex

Additional confirmation for TQ-G-quadruplex interactions was obtainedthrough fluorescence quenching titration. The following assay was usedto confirm binding interactions of TQ derivatives and their selectivitytowards human telomeric G-quadruplex.

To 3 ml of 1×10⁻⁷ M fluorescein labelled G-quadruplex(5′-Fl-AGGGTTAGGGTTAGGGTTAGGG-3′ (SEQ ID NO: 2), successive portions ofeach of the compounds TQs 1-8 (10⁻⁴ M) in Tris-KCl buffer, pH 7.4, wereadded. After each addition, the solution was stirred for 20 seconds,incubated for 3 minutes and scanned for its emission spectra at theFl-G-quadruplex emission λmax of 518 nm and excitation Amax of 494 nm.

Fluorescence intensity of Fl-G-quadruplex is quenched when a moleculebinds it near the fluorescence labelling flag molecule.

The changes in fluorescence emission of 5′-fluorescein-labelledG-quadruplex DNA at 518 nm using 494 nm as the maximum wavelength ofexcitation are shown in FIG. 3. Fluorescence of5′-fluorescein-labelled-quadruplex DNA showed a decrease in fluorescenceintensity with successive addition of the thymoquinone derivativecompounds. Quenching of 5′-fluorescein-labelled G-quadruplex isattributed to binding of the compounds in fluorescein proximity onFl-G-quadruplex DNA.

Circular Dichroism Titration

CD spectroscopy was used to follow conformational change of G-quadruplexDNA upon interaction with the thymoquinone derivatives. To 1 mlG-quadruplex DNA (4×10⁻⁶ M) in Tris-KCl buffer, pH 7.4, successiveamounts of each of the compounds TQ 1-8 (10⁻⁴ M) were added in ratios[drug]/[G-quadruplex] in the range of 0.2-15. After each addition, thesolution was well shaken, incubated for 3 minutes at room temperatureand scanned in the range 200-400 nm with 50 nm/min, band width 1 nm and3 accumulations. Samples' CD were subtracted from the blank and thenbase line corrected. Changes in CD bands at 293 nm were recorded versusdrugs' concentrations.

Interaction between the thymoquinone derivatives and G-quadruplex DNAwas also tested by CD titrations. Change in CD intensity duringtitration has been used to estimate the binding mode between the ligandand DNA. A decrease in CD intensity during DNA titration with ligand hasbeen correlated with an intercalation binding mode while an increase inintensity has been correlated with groove binding mode. Therefore,gradual decrease in CD intensity in the measurements may indicate aninteraction mode between the derivative compounds and G-quadruplex.

FIG. 4 shows the CD titration spectra of G-quadruplex DNA with compoundsTQ1-TQ8 (4 a-h). Decreases in CD intensity, without changes in bandspositions or shapes indicated a face π-π stacking intercalation processwithout conformational change in G-quadruplex during titration.

Melting Temperature Curves

In order to determine the stability of DNA upon complexation with ligandand its binding affinity, melting temperatures were determined.

Melting temperature curves for G-quadruplex and their TQs adducts wereconstructed using CD spectral measurements.

A 1 ml telomeric G-quadruplex (3.93×10⁻⁶ M) in Tris-KCl-buffer pH 7.4,was heated in 1-5° C. increments in the range 25-95° C. using 5 minutesincubation time intervals. CD spectra were recorded in the range 200-400nm using 50 nm/min, 1 nm band width and 3 accumulations at each point.CD spectra were baseline corrected against blank solution and CDintensities at 293 nm were plotted versus temperature.

Similarly G-quadruplex-TQ1-8 1 mL complex solutions that were 3.93×10⁻⁶M of G-quadruplex and 3.93×10−6 M of TQs were heated up to 95° C. andmeasured. The solutions were prepared by mixing equi-molar amounts ofG-quadruplex (27.3 μL, 1.44×10⁻⁴ M) with TQ compounds 1-8 (39.30 μL,1×10⁻⁴ M) in 1 mL KCl-buffer, pH 7.4. CD spectra were baseline correctedand CD intensities at 293 nm were plotted versus temperature.

FIG. 5 shows the melting temperature curves for G-quadruplex and itsTQs' complexes based on CD measurements. Table 3 shows the Tm valuesranged between 70 and 91° C. for G-quadruplex DNA and its TQs complexes.These values reflected Tm ranges between 6.0° C. and 21° C. Compound TQ8showed the highest Tm (91° C.) which is 21° C. higher than theG-quadruplex DNA.

These values are consistent with the binding constants shown in Table 3and indicate that the compounds of the invention act as stabilizers forG-quadruplex DNA.

Binding Affinity

Scatchard plots were used to determine the binding affinity of thethymoquinone derivative compounds to G-quadruplex based on fluorescencetitration, keeping the compounds concentration constant and varying DNAamounts.

Non-linear Scatchard plots were obtained for all TQ derivativessuggesting more than one type of dependant binding sites for all TQsmolecules on G-quadruplex DNA molecule. Dependant binding sites may havesynergistic (the first bound ligand encourage the next binding one) orantagonistic (the first bound ligand suppress the next binding one)effects on each other, a phenomenon known as the neighbor exclusioneffect. Non-linear regression based on a modified Scatchard equationgave the binding constants and number of binding sites shown in Table 3.Compound TQ8 has shown the highest binding constant (1.33×10⁷ M⁻¹) andcompound TQ5 has shown the lowest binding constant (7.76×10⁴ M⁻¹)

TABLE 3 Melting temperatures (Tm), binding constants (K) and number ofbinding sites (n) of G-quadruplex DNA upon interaction with various TQderivative compounds (TQ1-8). Complex Tm ° C. Δ Tm ° C. K (M⁻¹) NG-quadruplex DNA 70.0 0.00 — — G-quadruplex DNA- 79.0 9.0 1.13 × 10⁵ 2TQ1 G-quadruplex DNA- 76.0 6.0 5.67 × 10⁵ 1 TQ2 G-quadruplex DNA- 76.06.0 3.30 × 10⁵ 3 TQ3 G-quadruplex DNA- 76.0 6.0 9.52 × 10⁴ 3 TQ4G-quadruplex DNA- 77.0 7.0 7.76 × 10⁴ 1 TQ5 G-quadruplex DNA- 80.0 10.01.49 × 10⁶ 2 TQ6 G-quadruplex DNA- 77.0 7.7 1.17 × 10⁶ 2 TQ7G-quadruplex DNA- 91.0 21.0 1.33 × 10⁷ 2 TQ8

Selectivity of TQs Towards G-Quadruplex

Selectivity of TQ derivative compounds towards G-quadruplex DNA wasinvestigated using Fl-G-quadruplex (5′-Fl-AGGGTTAGGGTTAGGGTTAGGG-3′)(SEQ ID NO:2) in presence of the telomeric dsDNA or ct-DNA asinterfering species.

A 3 mL solution of TQ1-Fl-G-quadruplex complex was prepared by mixing30.00 μl of Fl-G-quadruplex (10⁻⁵ M) with 30 μl of TQ1 compound (10⁻⁵M). The solutions was made up to 3.00 ml using Tris-KCl-buffer pH 7.4,vortexed for 10 seconds, incubated for 3 minutes and then scanned forits fluorescence in the range 500-700 nm. The solution was then mixedwith 0, 10, 50 or 100 folds of telomeric dsDNA or ct-DNA, vortexed for10 seconds, incubated for 30 minutes at room temperature and scanned forits emission spectrum in the range 500-700 nm. The procedure wasrepeated for the TQ2-TQ8 compounds.

FIG. 6 shows change in fluorescence intensity of 5′-Fl-G-quadruplex TQscomplexes in presence of 0, 10, 50 and 100 folds of ctDNA (FIG. 6a ) andtelomere dsDNA (FIG. 6b ). The figures show that the fluorescence of5′-Fl-G-TQs complexes are either constant or a slightly increased uponaddition of ctDNA or telomere dsDNA indicating that both DNA species arenon or slightly-interfering. These experiments indicate good selectivityfor investigated thymoquinone compounds towards G-quadruplex DNA overctDNA and telomere dsDNA.

These results indicate that the thymoquinone derivatives of theinvention show good selectivity towards G-quadruplex DNA over duplex DNAand cytotoxicity over cancer cells, thereby suggesting that thecompounds would be helpful in the treatment of cancers.

The invention claimed is:
 1. A method of treating lung cancer, breastcancer, or colorectal cancer in a subject in need thereof, whereintreating lung cancer, breast cancer, or colorectal cancer does notinclude prophylactic treatment of lung cancer, breast cancer orcolorectal cancer, the method comprising administering to the subject aneffective amount of a compound of formula (I)

or a pharmaceutically acceptable salt or solvate thereof, wherein R₁ andR₂ are a C₁-C₆ alkyl, wherein R₁ and R₂ are different; X is NR₃R₄,wherein: R₃ is selected from H or —(CH₂)₂—OH; and R₄ is selected from Hor —(C₁-C₄alkyl)R₅, wherein: R₅ is selected from: a) —OH, b) phenyl,wherein phenyl is optionally substituted by 1-3 substituentsindependently selected from —CF₃, —F, —OCH₃, —NH₂ and —SO₂NH₂, c) a 5 or6 membered heterocyclic ring having 1 or 2 hetero atoms selected from 0and N, and wherein the heterocyclic ring is optionally substituted by1-2 substituents independently selected from —OH and CH₃, d) a ringsystem having the formula of:

and e) NR₆R₇, wherein: R₆ is selected from H or CH₃; and R₇ is selectedfrom CH₃, phenyl, and a ring system having the formula of:

wherein the ring system is optionally substituted by 1-2 substituent ofCH₃; and Y is H.
 2. The method of claim 1, wherein R₅ is selected from:a) —OH, b) phenyl, wherein phenyl is substituted by 1-3 substituentsindependently selected from —CF₃, —F, —OCH₃, —NH₂ and —SO₂NH₂, c) a 5 or6 membered heterocyclic ring having 1 or 2 hetero atoms selected from 0and N, and wherein the heterocyclic ring is optionally substituted by1-2 substituents independently selected from —OH and CH₃, d) a ringsystem having the formula of:

and e) NR₆R₇, wherein: R₆ is selected from H or CH₃; and R₇ is selectedfrom CH₃, phenyl, and a ring system having the formula of:

wherein the ring system is optionally substituted by 1-2 substituent ofCH₃.
 3. The method of claim 1, wherein R₃ and R₄ are not both H.
 4. Themethod of claim 2, wherein R₃ and R₄ are not both H.
 5. The method asclaimed in claim 1, wherein the subject is suffering from breast cancer.6. The method as claimed in claim 1, wherein the subject is sufferingfrom lung cancer.
 7. The method as claimed in claim 1, wherein thesubject is suffering from colorectal cancer.
 8. The method of claim 1,wherein R₁ and R₂ are selected from methyl and isopropyl.
 9. The methodof claim 4, wherein R₁ and R₂ are selected from methyl and isopropyl.10. The method of claim 1, wherein R₃ is H.
 11. The method of claim 1,wherein R₄ is —(C₁-C₄alkyl)R₅.
 12. The method of claim 1, wherein R₄ isH or —(C₁-C₄ alkyl)R₅, wherein R₅ is selected from OH, morpholinyl andphenyl, wherein the phenyl is optionally substituted with 1 or 2substituents selected from —CF₃, —F and —OCH₃.
 13. The method as claimedin claim 1, wherein the compound of Formula (I) is one of:5-Isopropyl-2-methyl-3-((2-morpholinoethyl)amino)-1,4-benzoquinone(TQ₁);5-Isopropyl-2-methyl-3-(4-trifluoromethylbenzylamino)-1,4-benzoquinone(TQ₂); 5-Isopropyl-2-methyl-3-(4-fluorobenzylamino)-1,4-benzoquinone(TQ₃); 5-Isopropyl-2-methyl-3-(benzylamino)-1,4-benzoquinone (TQ₄);5-Isopropyl-2-methyl-3-(3,5-ditrifluoromethylbenzylamino)-1,4-benzoquinone(TQ₅); 5-isopropyl-2-methyl-3-(2-hydroxyethylamino)-1,4-benzoquinone(TQ₆);5-isopropyl-2-methyl-3-(3,4-dimethoxybenzylamino)-1,4-benzoquinone(TQ₇); and 3-amino-5-isopropyl-2-methyl-1,4-benzoquinone (TQ₈).
 14. Themethod of claim 1, wherein the compound of Formula (I) is5-Isopropyl-2-methyl-3-((2-morpholinoethyl)amino)-1,4-benzoquinone(TQ₁).
 15. The method of claim 1, wherein the compound of Formula (I) is5-Isopropyl-2-methyl-3-(4-trifluoromethylbenzylamino)-1,4-benzoquinone(TQ₂).
 16. The method of claim 1, wherein the compound of Formula (I) is5-Isopropyl-2-methyl-3-(4-fluorobenzylamino)-1,4-benzoquinone (TQ₃). 17.The method of claim 1, wherein the compound of Formula (I) is5-Isopropyl-2-methyl-3-(benzylamino)-1,4-benzoquinone (TQ₄).
 18. Themethod of claim 1, wherein the compound of Formula (I) is5-Isopropyl-2-methyl-3-(3,5-ditrifluoromethylbenzylamino)-1,4-benzoquinone(TQ₅).
 19. The method of claim 1, wherein the compound of Formula (I) is5-isopropyl-2-methyl-3-(2-hydroxyethylamino)-1,4-benzoquinone (TQ₆). 20.The method of claim 1, wherein the compound of Formula (I) is5-isopropyl-2-methyl-3-(3,4-dimethoxybenzylamino)-1,4-benzoquinone(TQ₇).
 21. The method of claim 1, wherein the compound of Formula (I) is3-amino-5-isopropyl-2-methyl-1,4-benzoquinone (TQ₈).